This invention relates to digital data processing and, more particularly, apparatus and methods for transferring information between digital data processing functional units. The invention has applicability, for example, in transferring information between a host mainframe computer and a peripheral device.
Input/output controllers are known for transferring data from a host device to a peripheral device. U.S. Pat. No. 4,926,315, assigned to the assignee hereof, discloses an exemplary computer system in which an input/output controller is connected with peripheral devices via a dual bus structure. The controller applies duplicate strobe signals to the buses and, thereby, defines the timing of data (and control) signal transfers between the units. Each of the peripheral devices monitor the timing signals to initiate processing of information received on the buses.
In accord with related U.S. Pat. No. 4,939,643, the input/output controller initiates data transfer cycles between the peripheral devices by transmitting over the bus structure a cycle-initiating signal. Concurrently, it transfers a peripheral device addressing signal. If a fault occurs during transmission, the peripheral devices generate a WAIT signal, which delays further transmissions by the controller on the buses.
Commonly assigned U.S. patent application Ser. No. 743,992 U.S. Pat. No. 5,379,381 discloses an input/output controller that transfers information with a peripheral device in both direct memory access (DMA) and processor command (PIO) modes. The controller has DMA circuitry and PIO circuitry that work together, during DMA transfers, to interleave data and command transmission without intervention of the local processor.
While the controllers described in the aforementioned patents and patent applications have proven very effective, there remains a need for still better data transfer apparatus that can be used, for example, in an input/output controller.
It is, accordingly, an object of this invention to provide an improved method and apparatus for transferring information between digital data processing functional units. Another object is to provide improved mechanisms and processes for input/output control.
A related object is to provide improved input/output control apparatus and methods that facilitate the rapid transfer of data to functional units, such as peripheral devices, while minimizing the complexity of attendant software and hardware mechanisms.
Still another object of the invention is to provide an inter-functional unit data transfer mechanism with enhanced immunity from timing errors.
Other general and more specific objects of this invention will in part be obvious and will in part appear hereinafter.